new() 约束对类定义有什么作用? [英] What does the new() constraint do on a class definition?

问题描述

我看到了这个代码示例，想知道 new() 约束的目的是什么:

I saw this code example and was wondering what the purpose of the new() constraint was:

public class Client<T> : IClient where T : IClientFactory, new()
{
    public Client(int UserID){ }
}

推荐答案

这就是所谓的‘新’约束".这里是文档.

That's called a "'new' constraint". Here's the documentation on it.

新约束指定泛型类声明中的任何类型参数都必须具有公共无参数构造函数.要使用新的约束，类型不能是抽象的.

The new constraint specifies that any type argument in a generic class declaration must have a public parameterless constructor. To use the new constraint, the type cannot be abstract.

(强调我的)

基本上，每当您在类中的某处创建新的 T 时都需要它，以确保您只能传入编译器可以 创建一个新的实例.

Basically, you need it whenever you're creating a new T somewhere in the class, to ensure that you're only able to pass in things which the compiler can create a new instance of.

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